The objectives of the grant are to define the short and long term effects of 25-hydroxy-vitamin D (25-OHD) deficiency, specifically focusing on 6 defined infant problems and to begin to define rational prophylaxis. To date, 80 premature and 35 SGA infants have been prospectively followed and 6 infants with late neonatal hypocalcemia and 30 SIDS infants have been studied. The study has defined 1) a high incidence of early neonatal hypocalcemia without significant correlation to low 25-OHD, 2) no evidence for 25-OHD deficiency in late neonatal hypocalcemia but evidence for low PTH, 3) a strong association between 25-OHD deficiency and osteopenia, fractures, and rickets plus hypocalcemia (P less than .01) and hypophosphatemia (P less than .01) at 3 months of age, 4) a significant (P less than .02) correlation between 3 month 25-OHD and 1 year height percentile correlated for gestation with a fourth of infants less than third percentile for height at 1 year, 5) a 25 percent incidence of abnormal upper incisors plus delayed eruption of teeth corrected for gestational age, 6) no evidence for a deficiency of serum 25-OHD in SIDS; however, confirmation of costochondral junction abnormalities. This grant will a) continue long term follow-up of infants currently enrolled in the study; b) begin to evaluate short and long term effectiveness of three alternative treatment trials; 1) higher dose vitamin D, 2) 25-hydroxycholecalciferal supplementation, and 3) calcium supplementation; c) further explore the roles of elevations of calcitonin and depression of PTH in early and late neonatal hypocalcemia; d) use tissue measurements to define whether total body deficiencies of calcium, magnesium, copper, and zinc do exist in premature infants and SIDS; e) further define histologically the normal process of in utero bone formation and define how premature infants with osteopenia and SIDS infants differ from that process.